Spring in the southern hemisphere of Mars brings with it mystery. Every year, without fail, strange fan-like markings and dark spots appear on the ice cap at the Martian South Pole and disappear as the red planet's summer wanes. New observations prove the spots cannot just be the ground revealed by thawing ice. Instead, scientists say, they are the result of high-pressure gas geysers that arise when the sun warms layers of dust and sand beneath carbon dioxide frozen during the Martian winter. The warming particles cause the CO2 to explosively change from solid to gas and carry them away to form the unique shapes on the more permanently frozen water ice beneath. A paper detailing the findings appears today in the journal Nature.